From: peterz@infradead•org (Peter Zijlstra)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 1/2] arm64: atomics: fix use of acquire + release for full barrier semantics
Date: Tue, 4 Feb 2014 17:43:08 +0100 [thread overview]
Message-ID: <20140204164308.GA5002@laptop.programming.kicks-ass.net> (raw)
In-Reply-To: <1391516953-14541-1-git-send-email-will.deacon@arm.com>
On Tue, Feb 04, 2014 at 12:29:12PM +0000, Will Deacon wrote:
> @@ -112,17 +114,20 @@ static inline int atomic_cmpxchg(atomic_t *ptr, int old, int new)
> unsigned long tmp;
> int oldval;
>
> + smp_mb();
> +
> asm volatile("// atomic_cmpxchg\n"
> -"1: ldaxr %w1, %2\n"
> +"1: ldxr %w1, %2\n"
> " cmp %w1, %w3\n"
> " b.ne 2f\n"
> -" stlxr %w0, %w4, %2\n"
> +" stxr %w0, %w4, %2\n"
> " cbnz %w0, 1b\n"
> "2:"
> : "=&r" (tmp), "=&r" (oldval), "+Q" (ptr->counter)
> : "Ir" (old), "r" (new)
> : "cc", "memory");
>
> + smp_mb();
> return oldval;
> }
>
Any particular reason atomic_cmpxchg() doesn't use the proposed rel + mb
scheme? It would be a waste to have atomic_cmpxchg() be more expensive
than it needs to be.
next prev parent reply other threads:[~2014-02-04 16:43 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-04 12:29 [PATCH 1/2] arm64: atomics: fix use of acquire + release for full barrier semantics Will Deacon
2014-02-04 12:29 ` [PATCH 2/2] arm64: asm: remove redundant "cc" clobbers Will Deacon
2014-02-19 17:05 ` Catalin Marinas
2014-02-04 16:43 ` Peter Zijlstra [this message]
2014-02-04 17:16 ` [PATCH 1/2] arm64: atomics: fix use of acquire + release for full barrier semantics Will Deacon
2014-02-19 17:05 ` Catalin Marinas
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